A stepping motor is able to change the position and speed of its rotor in response to a pulse signal that is input from an external device. Stepping motors are widely used in devices such as printers, scanners, copiers, and multifunction products. However, as compared to e.g. brushless DC motors, stepping motors have problems such as significant vibration and noise, low efficiency of energy conversion, and loss of synchronization.
Japanese Laid-Open Patent Publication No. 2015-19563 discloses an image forming device having a brushless DC motor instead of a stepping motor. Upon receiving a pulse signal that designates the position of the rotor, the brushless DC motor in this device rotates the rotor by a unit step angle for each pulse. A signal (rotary position detection signal) indicating the position of the rotor of the brushless DC motor is generated by converting a magnetic pole phase signal which is output from the brushless DC motor. This rotary position detection signal is a two-phased pulse sequence which is equivalent to a signal that is output from a known rotary encoder.